1. Field of the Invention
The present invention relates to a developing device used for visualizing an electrostatic latent image formed on an image bearing member of an image forming apparatus, and to a developer amount restricting member for restricting an amount of developer on a developer bearing member.
2. Related Background Art
In an electrophotographic image forming apparatus, an electrostatic latent image formed on an image bearing member is visualized by developing the latent image with using developer in a developing device.
As shown in FIG. 4, in this developing device, a developing sleeve 103, as a developer bearing member, rotating in the direction shown by the arrow bears on its surface toner (developer), not shown in the figure, and conveys the toner to a developing portion opposite to an image bearing member, and on the way to the developing portion the toner is made to pass between the developing sleeve 103 and a rubber or metallic blade for restricting the amount of developer (a developing blade) 104 which is in contact with the surface of the developing sleeve 103 so that the amount of the toner to be conveyed will be restricted, thus a thin layer of the toner is formed on the developing sleeve 103 and the toner is imparted with a triboelectric charge (triboelectricity) suitable for developing a latent image.
For a rubber developing blade 104, a simple rubber sheet of, for example, polyurethane rubber is sometimes used, but often used is the type in which a rubber sheet 104b as a triboelectricity charging member is supported by a metalic supporting member 104a.
In recent years it has been an important problem to improve the performance of a developing blade, such as triboelectrifying property and toner fusing preventive property, so as to deal with various types of toner including the latest one.
Recently there appear various types of toner, such as a low meltpoint toner (a sharp melt toner) which is provided with a property to fix at a lower temperature than a conventional one in terms of saving energy, toner (non-magnetic toner) which is provided with no magnetism to keep up with coloration of printing, or polymer toner.
These types of toner are required to exhibit an especially high triboelectrifying property. For example, increasing the contact pressure of the developing blade 104 against the developing sleeve 103 ensures a requisite triboelectrifying property.
An increased contact pressure, however, makes it easier for toner to adhere to the surface of the developing blade 104, which leads to formation of deposit of toner especially at the end portions of the developing blade, and hence a remarkable occurrence of toner fusing. Occurrence of toner fusing on the surface of the developing blade leads to a reduction in triboelectrifying property of the developing blade, and hence an insufficiently charged toner, which may present a threat of leakage of toner from the developing device, resulting in contamination of not only the inside of the developing device but the whole inside of the image forming apparatus.
One possible way to solve this problem might be to use a surface material which exhibits sufficient triboelectrifying property even under a light contact pressure; for example, for negative toner, it would be better to use nylon-based resins, which tends to be charged positively in itself, for a triboelectrifying member 104b. However, use of a developing blade whose surface material is high in flatness creates a difference in contact pressure between its longitudinal central portions and end portions. This limits the selection of a developing blade which can realize the contact pressure under which a good triboelectrifying property is obtained. Thus great accuracy is required in setting up a developing blade etc., which may cause an increase in manufacturing cost of not only a developing device but of an image forming apparatus.